1. Field of the Invention
The invention relates generally to earth boring bits of both the fixed cutter or drag bit variety as used in industry, mining and construction and of the rolling cutter variety used in oil/gas exploration and the like. More specifically, the invention relates to a heat management system and methods for stress relieving cutting tool inserts and for improving drilling performance.
2. Prior Art
Polycrystalline diamond (PCD) is becoming more widely used in making cutting tool inserts. PCD materials are formed of fine diamond powder sintered by intercrystalline bonding under high temperature/high pressure diamond synthesis technology into a predetermined layer or shape;
and such PCD layers are usually bonded to a substrate of xe2x80x9cprecementedxe2x80x9d tungsten carbide to form a polycrystalline diamond compact (PDC)or insert (e.g. cutting element). The term xe2x80x9chigh density ceramicxe2x80x9d (HDC) is sometimes used to refer to a mining tool having an insert with a PCD layer. The term xe2x80x9cchemical vapor depositionxe2x80x9d (CVD) is a form of pure PCD used for inserts, and xe2x80x9cthermally stable productxe2x80x9d (TSP) is another form of pure diamond that can be bonded to a carbide substrate or directly to a steel bit body using new vacuum furnace techniques by GE and Sandia Laboratories. Still other superhard surfacing and layered materials, such as xe2x80x9cadvanced diamond composite (ADC)xe2x80x9d and xe2x80x9cnitridexe2x80x9d compositions of titanium (TiN) and carbon (C2N2), are gaining acceptance in the mining field. All such superabrasive or superhard materials - PCD, TSP, CVD, ADC and nitride compositions are applicable to the present invention, and the terms xe2x80x9cPCDxe2x80x9d and xe2x80x9cPDCxe2x80x9d shall be considered inclusive of all.
The principal types of drill bits used in rotary drilling operations are roller bits and drag bits. In roller bits, rolled cones are secured in sequences on the bit to form cutting teeth to crush and breakup rock and earth material by compressive force as the bit is rotated at the bottom of the bore hold as in oil/gas exploration. In drag bits, PCD or like cutting elements on the bit act to cut or shear the earth material. The action of some flushing medium (fluid drilling mud, water, a compressed air or vacuum system) is important in all types of drilling operations to cool the cutting elements and to flush or transport cuttings away from the cutting site. It is important to remove cuttings to prevent accumulation of debris that will interfere with the continued crushing or cutting action of the bit, and the cooling action is particularly important in the use of PCD cutters to prevent carbon transformation of the diamond material at about 1250xc2x0 F.
The prior art is replete with various cutting element designs directed by a desire to form structurally stronger, tougher and more wear-resistance and fracture-resistant tools. It is well-known for example, that superabrasive (PCD) cutting elements can fail caused by the fact that the materials comprising the superabrasive portion, or diamond table, and the substrate have different coefficients of thermal expansion, elastic moduli and bulk compressibilities. After formation of such cutting elements by known high temperature and high pressure techniques, the table and substrate materials subsequently shrink at different rates during cooling thereby resulting in internal residual stresses in the superabrasive table, notably in the vicinity of the interface between the table and the substrate. Consequently, the diamond table material tends to be in residually stressed tension while the substrate material tends to be in residually stressed compression prior to being subjected to cutting loads experienced during drilling operations which may result in fracturing of the cutting element. Such residual stresses in the cutting element may also provoke delamination of the table from the substrate or delamination in the table itself under extreme drilling temperatures and pressures. Various solutions have been suggested to address the problems of residual stress and delamination. For instance, cooperating table and substrate configurations thought to address these issues are disclosed in the following literature:
U.S. Pat. No. 4,604,106 to Hall et al
U.S. Pat. No. 5,007,207 to Phaal
U.S. Pat. No. 5,120,327 to Dennis
U.S. Pat. No. 5,351,772 to Smith
U.S. Pat. No. 5,355,969 to Hardy et al
U.S. Pat. No. 5,494,477 to Flood et al
U.S. Pat. No. 5,544,713 to Dennis
U.S. Pat. No. 5,566,779 to Dennis
U.S. Pat. No. 5,605,199 to Newton
When PCD inserts are initially made, the diamond table is highly stressed, as stated, and manufacturers now attempt a stress relief process at about 950xc2x0 F. Nonetheless, residual stress and insert failure continue to be an industry concern, and the following additional prior art indicates that insert configuration (particularly at the interface) continues to be the primary industry direction.
U.S. Pat. No. 5,950,745 to Ingmarsson
U.S. Pat. No. 5,954,147 to Overstreet et al
U.S. Pat. No. 5,971,081 to Chaves
U.S. Pat. No. 6,026,919 to Thigpen et al
Thus, prior art attempts to incorporate diamond or other super-hard materials as the cutting structure of earth boring tools have presented design and performance problems that heretofore have not been satisfactorily addressed.
My prior U.S. Pat. Nos. 5,180,022; 5,303,787 and 5,383,526 disclose substantial improvements in HCD roof drill bits using PCD cutting elements constructed in a non-coring arrangement, and also teach novel drilling methods that greatly accelerate the speed of drilling action and substantially reduce bit breakage and change-over downtime. These prior HCD non-coring drill bits are capable of drilling over 100-300 holes of 4 foot depth with a single bit and in shorter times with less thrust than the standard carbide bits in hard rock or sandstone formations having a compressive strength of 22,000-28,000 psi. Although these prior HCD bits easily drilled through such earth structures, it was discovered that some drill bits might plug in drilling through mud seams and other soft or broken earth formations and PCD cutting inserts may even shatter in working through stratas of extremely hard or fractured earth conditions believed, in part, to be due to residual stress conditions in the cutting elements. My U.S. Pat. No. 5,535,839 discloses another HCD roof drill bit designed to operate more efficiently in broken and muddy earth formations, but residual stress in these radially domed cutting elements may still shorten the useful life of such tools.
All of these prior HCD drill tools used wet drilling techniques in which substantially quantities of water were employed according to conventional drilling practices. However, comparative tests conducted in three states determined that the amount of water required to wet drill with HCD rotary bits may be reduced from a conventional range of 9-18 gallons per minute down to about 1-3 quarts per minute when atomized into an air mist that effectively scours and cools the PCD cutting inserts of my patented roof drill bits. Thus, my U.S. Pat. No. 5,875,858 discloses a system for greatly reducing the amount of water needed for effective bore hold flushing, although heat management to prevent carbon transformation may still be a problem with some PCD cutting element configurations and, heretofore, vacuum (dry) drilling to evacuate cutting from the drill site has not been a practical option, especially with TSP, PCD and CVD insert tools.
The invention is embodied in an earth boring tool comprising a bit body having a rotatable working head portion with a cutter element having a wear table of superhard material bonded to a substrate member, and wherein the superhard and substrate materials have different coefficient properties creating a stress condition at their interface during bonding and wherein the cutter elements are stress relieved in situ on the bit body by low temperature annealing for a preselected time, and in which the cutter elements and bit body head portion are constructed and arranged for heat management in a dry, vacuum drilling operation. The invention further involves the heat management system and method of the stress relief process of heat annealing PCD cutter elements in situ, either alone or with a subsequent cryogenic tempering process.
It is the principal object of the present invention to provide an earth boring tool with an improved superhard wear table that will extend the useful life of the tool.
Another important object of the invention is to provide a superabrasive cutter element in which the problem of differential coefficient expansion therein is obviated.
Another object is to provide a bit having a superabrasive wear table constructed and arranged to dissipate the heat generated during boring operations using a dry vacuum process of removing cutting debris.
Another object is to provide a clean bore hole to facilitate heat management and removal of cuttings using a dry vacuum system.
Still another object is to provide a heat management system and method for stress relieving the superhard cutter elements for preventing delamination and other premature failure attributed in the past to such stress conditions.
Still another object is to provide a heat management system and method for constructing and operating superhard surfaced cutter elements permitting drilling with vacuum debris removal systems.
Still another object is to provide an HCD bit using PCD cutting elements and an optimum supporting body, that minimizes torsional stress, prevents heat build-up with either wet or dry drilling techniques, drills faster and reduces respirable dust.
These and still other objects and advantages will become more apparent hereinafter.